1. Field of the Invention
The present invention relates to apparatus for and a method of scheduling cell forwarding for use specifically in an asynchronous transfer mode (ATM) network, for example.
2. Description of the Background Art
To the scheduling of forwarding cells in the ATM transferring systems, the round robin scheduling is known to be applicable. For example, H. Shimonishi, et al. xe2x80x9cList-Based Weighted Round Robin Schedulingxe2x80x9d 1997 Society Conference of The Institute of Electronics, Information and Communication Engineers of Japan, B-6-44, 1997, discloses an application of the weighted round robin (WRR) scheduling to transmitting cells in the ATM transfer systems. The weighted round robin scheduling is commonly applied to ATM switches as a scheduling system which ensures the minimum bandwidths to be established appropriately for respective queues of waiting cells to be forwarded.
With the commonly used weighted round robin scheduling, however, no account has been taken of delay encountered in transmitting cells. The cell delay is one of the most important factors influencing the quality of transmission along with the bandwidth. In order to control the delay of cells, the delay factor has to be taken account of in scheduling the forwarding of cells.
It is therefore an object of the present invention to provide an apparatus for and a method of scheduling cell forwarding with the delay of cells to be forwarded effectively controlled.
According to the present invention, the delay of cells to be forwarded is effectively controlled in scheduling cell forwarding by means of the round robin scheduling with a weight adaptively adjusted in response to the traffic and the controlled delay of cells to be forwarded.
In accordance with the present invention, an apparatus for scheduling cell forwarding for use in an ATM network for switching ATM cells, comprises: a plurality of queues each provided for one of classes of transmission quality for queuing up an ATM cell in corresponding one of the classes which is required by the ATM cell; a cell classifying circuit for receiving an ATM cell and classifying the ATM cell received to one of said plurality of queues in accordance with the class required by the ATM cell; a status circuit for detecting a status of said plurality of queues and storing status data representative of the status detected; and a scheduling circuit operative in response to said status circuit for determining when the ATM cell queuing up in said plurality of queues is to be forwarded.
Further in accordance with the invention, a method of scheduling cell forwarding for use in an ATM network for switching an ATM cell, comprising the steps of: preparing a plurality of queues each for one of classes of transmission quality for queuing up an ATM cell in corresponding one of the classes which is required by the ATM cell; receiving an ATM cell; classifying the ATM cell received to one of the plurality of queues in accordance with the class required by the ATM cell; detecting a status of the plurality of queues and storing status data representative of the status detected; and determining, in response to the status data, when the ATM cell queuing up in the plurality of queues is to be forwarded.
More specifically, in an ATM network, ATM cells received are classified to the queue appropriate to the service classes required by the ATM cells. The status registers manage the controlled delay of the ATM cells for the service classes and the queue length of the ATM cells which queue up in the queues. On the basis of the controlled delay and the queue length, the scheduler adaptively determines a weight, on the basis of which the ATM cells queuing up in the queues are to be forwarded to thereby effectively control the delay of ATM cells to be forwarded.